COVID-19: Pfizer, AstraZeneca efficacy significantly reduced against omicron, says UK health agency 

Omicron is displaying growth advantage over delta and is poised to become dominant variant in UK

By Taran Deol
Published: Monday 13 December 2021

The United Kingdom is under a “tidal wave” of cases of the novel coronavirus disease (COVID-19) linked to the new variant omicron, according to Prime Minister Boris Johnson. 

The nation recorded 1,239 new omicron cases on Sunday taking the national variant tally to 3,137, according to official data. The biggest worry, according to health experts, is that the latest mutations may render the two widely-used vaccine candidates — by Pfizer Inc and AstraZeneca Plc — less effective. 

The UK Health Security Agency’s (UKHSA) risk analysis for omicron puts growth advantage and immune evasion under the ‘red’ category, transmissibility under ‘amber’ and does not classify infection severity citing insufficient data. The health agency raised the overall COVID-19 alert in the nation to ‘5’ from ‘4’. 

The new ‘variant of concern’ (VOC) is displaying “a growth advantage over the delta” variant, which essentially means that it will likely take over and become the predominant variant in the country, according to UKHSA. 

Vaccine and natural infection-derived immunity reduces significantly against preventing omicron infection, the health agency noted. On its transmissibility factory, it said the new VOC is “at least as transmissible as delta.” 

Data on severe disease is awaited but vaccines have been more effective in preventing severe disease than mild infection in the case of previous variants, the national health body wrote.

The report published December 10, 2021 stated: 

There was a 20- to 40-fold reduction in neutralising activity by Pfizer 2-dose vaccine sera for omicron compared to early pandemic viruses. A greater reduction in activity was seen for AstraZeneca 2- dose sera, and for a high proportion of such sera, neutralising activity fell below the limit of quantification in the assay.

A booster shot of Pfizer “irrespective of primary vaccination type”, however, resulted in an increase in neutralising activity, touching 70-75 per cent, the report showed. 

UK will begin administering booster shots for individuals above the age of 18 this week, to be taken three months after their second dose. 

Currently, 68 per cent of the country's population is fully vaccinated, while 6.6 per cent are partially vaccinated. The weekly cases and deaths rose 12 per cent and 1 per cent, respectively, in the last seven days. 

“It will be a few weeks before (vaccine) effectiveness against severe disease with omicron can be estimated. However, based on this experience, it is likely to be substantially higher than the estimates against symptomatic disease,” UKHSA noted.

The vaccine efficacy analysis was conducted for 56,439 delta and 581 omicron cases. The number of omicron cases are still fewer than delta but the new VOC is feared to level delta prevalence by mid-December, if it continues to spread at the current rate. 

Very few omicron cases in the country have a travel history or met with someone who has a travel history, hinting at community transmission, the report showed. There was a 3-8 fold increase in reinfections — 7 per cent (25 out of 361) omicron cases and 0.4 per cent (336 out of 85,460) delta cases were reinfections, according to the analysis.


While this is still early data, household transmission has also significantly increased between omicron and delta — 19 per cent of omicron cases resulted in household outbreaks, in comparison to 8.5 per cent of delta cases, according to the UK health agency. 

Subscribe to Daily Newsletter :

Comments are moderated and will be published only after the site moderator’s approval. Please use a genuine email ID and provide your name. Selected comments may also be used in the ‘Letters’ section of the Down To Earth print edition.